A known recording head described in Japanese Patent Laid-Open No. 2002-79672 includes two nozzle rows, each row including a plurality of nozzles aligned at a regular pitch, and an ink inlet provided between the nozzle rows. By providing nozzles on both sides of the ink inlet so that nozzles in one nozzle row are offset by a half pitch from the nozzles in the other nozzle row, the nozzle density of a known recording head having such a structure is two times the nozzle density of a recording head including only one nozzle row.
FIG. 1 is a perspective plan view illustrating the inlets and their periphery of a known recording head. As illustrated in FIG. 1, on both sides of an ink inlet 1500, a plurality of outlets 1100 are aligned at a predetermined pitch in the longitudinal direction of the ink inlet 1500 (i.e., the vertical direction in the drawing). The ink inlet 1500 communicates with nozzles that each include one of the outlets 1100 and an ink channel 1300. In this way, ink is supplied from the ink inlet 1500 to each of the outlets 1100.
More specifically, the ink channel 1300 is constituted of a pressure chamber 1302 that includes a recording element 1400 having a heating resistor and a transporting path 1301 for supplying ink to the pressure chamber 1302. The pressure chamber 1302 is a space where discharge energy is applied to ink. The pressure chamber 1302 must be large enough to enable appropriate discharge of ink from the outlet 1100.
Japanese Patent Laid-Open No. 2002-374163 describes a recording head including recording elements each having a heating resistor, a driver (for example, a transistor) for driving the recording element, and a logic circuit for selectively driving the driver in accordance with image data.
A commercialized version of the recording head shown in FIG. 1 has a nozzle density of 1,200 dots per inch (dpi) per color (i.e., the nozzle density for each nozzle row is 600 dpi) and an ink droplet volume of 2 picoliters (pl) for each ink droplet discharged from the outlets 1100. However, in order to produce high quality images, a recording head capable of discharging droplets having even smaller volumes is in need. To obtain such a recording head, the nozzle density may be increased while the volume of the droplets discharged from the nozzles is decreased. More specifically, for example, the discharge amount of a recording head may be less than 2 pl and the nozzle density of two nozzle rows included in the recording head may be 2,400 dpi, wherein the nozzle density of each nozzle row is 1,200 dpi.
However, since the outlets 1100 of the recording head having the above-described nozzle density are aligned in rows along the longitudinal direction of the ink inlet 1500, it becomes difficult to maintain the thickness of the walls between each ink channel 1300. As a result, the reliability of the recording head is reduced.
To solve this problem, a recording head according to an embodiment of the present invention includes nozzle rows having outlets 1100 arranged in a staggered pattern, as illustrated in FIG. 2. The recording head shown in FIG. 2 is structured so that the distances from the ink inlet 1500 to adjacent outlets 1100 alternate. The ink channels 1300 corresponding to the outlets 1100 disposed closer to the ink inlet 1500 include transporting paths 1301 and pressure chambers 1302. Ink channels 1305 corresponding to the outlets 1100 disposed further away from the ink inlet 1500 include transporting paths 1306, wherein each of the transporting paths 1306 are interposed between adjacent pressure chambers 1302.
When the outlets 1100 are disposed in a staggered pattern with respect to the ink inlet 1500, as described above, the lengths of transporting paths 1301 and the transporting paths 1306 differ. Since the nozzle density is expected to be high (i.e., the pitch of the nozzles is expected to be small), the difference in the lengths of the transporting paths causes a significant difference in the channel resistance at the rear area of the heating resistors. Furthermore, the heating resistors disposed closer to the inlet 1500 are shaped as rectangles extending in the longitudinal direction of the channels so as to increase their heating areas. The rectangular shape of the heating resistors causes the difference in the lengths of the transporting paths to become even more prominent.
This difference in the lengths of the transporting paths causes a difference in the refilling speed. It is difficult to obtain a satisfactory refilling speed in the liquid channels corresponding to the heating resistors disposed further away from the inlet 1500.
The difference in the channel resistance also causes a difference in the discharge performance of the outlets. A significant difference in the discharge performance of each outlet may cause a decrease in image quality.
Such problems are not only typical to recording heads configured to discharge droplets of the same volume from the nozzles. For example, a recording head including both nozzles for discharging droplets of a relatively large volume and nozzles for discharging droplets of a relatively small volume may also have the same problems when the nozzle density is increased. These problems are not limited to recording heads configured to carry out recording by discharging ink. The same problems may be experienced also in liquid discharge heads used in the technical fields other than recording (e.g., color filter manufacturing and circuit pattern drawing) that discharge liquid using recording elements including heating resistors.